First off, consider raising grain as a "mining" process. When grain is harvested, it removes essential nutrients from the soil (mines out major and minor minerals). That process is not infinite, but will surely deplete the soil. In order for soil to continue its production, these nutrients must be replaced. Commercial fertilizers can replace the larger, or major, nutrients, but little is known about trace elements. Trace elements found in grains are essential to good grain production as well.

So, does it make sense to burn your food stock, and future food production? I have a problem with that.